Polyimides are an important class of polymeric materials and are known for many desirable performance properties. These properties include high glass transition temperatures, good mechanical strength, high Young's modulus, good UV durability, and excellent thermal stability. As a result of their favorable properties, polyimide compositions have become widely used in many industries, including the aerospace industry, the electronics industry and the telecommunications industry.
In the electronics industry, polyimide compositions are used in applications such as forming protective and stress buffer coatings for semiconductors, thermal insulating coatings, dielectric layers for multilayer integrated circuits and multi-chip modules, high temperature solder masks, bonding layers for multilayer circuits, final passivating coatings on electronic devices, and many others. In addition, polyimide compositions may form dielectric films in electrical and electronic devices such as motors, capacitors, semiconductors, printed circuit boards and other packaging structures. Polyimide compositions may also serve as an interlayer dielectric in both semiconductors and thin film multichip modules. The low dielectric constant, low stress, high modulus, and inherent ductility of polyimide compositions make them well suited for these multiple layer applications. Other uses for polyimide compositions include alignment and/or dielectric layers for displays, and as a structural layer in micromachining applications. Electronic components using polyimide films are used in many other industries.
Polyimides also have many different uses in the aerospeace industry, the automotive industry, the rail industry, the natural gas industry, and others. Polyimides can be used as high temperature adhesives, thermal insulations, protective coatings or layers, membranes, gaskets, and a wide variety of other uses.
The increased complexity of the applications for polyimides has created a demand to tailor the properties of such polyimides for specific applications. Compounds, pigments, substances, or other moieties incorporated into a polyimide or other polymer can change the properties of that polymer. Many different compounds can be added to polymers to change the polymer properties, and these compounds can be added in different ways. The added compounds can be covalently bonded to the polymer, dissolved or suspended in the polymer, or otherwise included in the polymer (such as with ionic bonding.) Often, an added compound will change more than one property, so controlling one property independently from a second property can be challenging. Some polymer uses require specific ranges for several different properties, and controlling the measured value of one property can co p e with controlling the value of a different property.
Pigment additives, such as carbon black, titanium dioxide, boron nitride, boron oxide covered by aluminum nitride, aluminum oxide, silicon oxide, aluminium powder, silicon dioxide, silicon carbide, aluminium nitride, calcium phosophide, barium titanium oxides, other metal oxides and metal nitrides are commonly incorporated into polyimide films to increase film opacity and so-called “hiding” effect, where it is important in the end-use application to obscure underlying components, structures, or electronic circuitry. However, even though the use of insoluble additives are effective at rendering films translucent or opaque in appearance and providing films with the desired optical properties, the inclusion of such additives may adversely affect other critical properties. For example, the dielectric breakdown voltage of the film is substantially decreased with the inclusion of metal oxide and carbon black particles. The electrical conductivity, dielectric constant, and radiofrequency (RF) absorption are both substantially increased with the use of carbon black additives, neither of which is desired for electronics applications. Additionally, the inclusion of metal oxides requires additional processing steps and manufacturing equipment which are costly to install and expensive to operate. There remains a need for an insulative black opaque black polyimide film with good dielectric properties that is easily manufacturable.
In contrast, the polyimide polymer containing the dye(s) describe herein have numerous advantages over the polyimide polymers made using carbon-black, including easier methods of synthesis as the soluble black dye is easier to incorporate in the polymer than carbon-black, reduced conductivity, reduced radio wave absorption, improved breakdown voltage and a lower than typical dielectric contant.